What is the prescription topical cream, such as fluorouracil (5-FU), used to draw potential skin cancers to the surface?

Topical Prescription Creams for Skin Cancer Treatment

The prescription topical cream designed to draw potential skin cancers to the surface is 5-fluorouracil (5-FU), available in concentrations of 5% (and also 0.5% and 4%), which works by inhibiting DNA synthesis in rapidly dividing abnormal cells, causing them to become inflamed and visible before clearing. 1

Mechanism of Action

5-FU functions by inhibiting thymidylate synthase, an enzyme essential for DNA synthesis, and may also interfere with RNA formation and function. 1 This selective action on rapidly dividing cells causes precancerous and cancerous lesions to become inflamed, eroded, and crusted as they are "drawn out" before resolving. 1

FDA-Approved Indications

According to the FDA label, fluorouracil cream is indicated for:

• Multiple actinic (solar) keratoses - all concentrations 2
• Superficial basal cell carcinomas - 5% strength only, when conventional methods are impractical (multiple lesions or difficult treatment sites), with approximately 93% success rate 2

The FDA explicitly states that 5-FU has not been proven effective in other types of basal cell carcinomas beyond superficial variants. 2

Alternative Topical Agent

Imiquimod 5% cream is another prescription topical that works differently - as an immune response modifier rather than a chemotherapeutic agent. 1 It stimulates both innate and acquired immune systems to target abnormal cells. 1 However, imiquimod is 19 times more expensive than 5-FU by weight and produces similar side effects. 1

Standard Treatment Regimens

For Actinic Keratoses:

• 5% 5-FU cream: Twice daily for 4 weeks is the most common regimen 1
• 0.5% 5-FU with 10% salicylic acid: Once daily for 7-28 days 1
• Less frequent application (pulsed therapy) can be used to reduce morbidity while maintaining some efficacy 1

For Squamous Cell Carcinoma In Situ (Bowen's Disease):

• 5% 5-FU cream: Once daily for 1 week, then twice daily for 3 weeks, achieving 83% complete response at 3 months 1, 3
• May be repeated at 6 weeks if clinically indicated 3

For Superficial Basal Cell Carcinoma:

• 5% 5-FU cream: Twice daily for up to 12 weeks, with mean clinical cure time of 10.5 weeks and 90% histologic cure rate 4

Critical Clinical Considerations

Maximum treatment area: Do not exceed 500 cm² for 5% 5-FU due to toxicity concerns. 1

Important contraindications and cautions:

• Hyperkeratotic lesions - drug cannot penetrate thick keratin layer 1, 5
• Poor healing sites (especially lower legs in elderly) - use with extreme caution and supervision 1, 5
• Digital, periungual, and nail bed lesions - generally poor choices 1, 5
• Immunocompromised patients - less effective 5
• Recurrent or invasive lesions - 5-FU should NOT be used; these require surgery or radiotherapy 5

Expected Side Effects and Management

Patients will experience local inflammation as the treatment "draws out" abnormal cells:

• Erythema (redness) - expected and indicates drug activity 1
• Crusting, oozing, and soreness with local swelling 1
• Erosions or ulceration (10.2% with imiquimod, similar with 5-FU) 1

Management strategies:

• Start with small treatment areas (4-10 cm²) to establish tolerance 1
• Take breaks in treatment if reaction is excessive 1
• Reduce frequency of application 1
• Apply thin emollient 1
• Use weak topical steroid for excessive reactions 1

Common Pitfall to Avoid

Do not use 5-FU for recurrent skin cancers or as definitive treatment for invasive lesions. The British Association of Dermatologists explicitly recommends 5-FU only for primary, low-risk lesions. 5 For recurrent or poorly defined lesions, Mohs surgery is first-line treatment, with radiotherapy as an alternative when surgery is not feasible. 5

Efficacy Ranking

A Cochrane meta-analysis ranked 5-FU at the top for efficacy among all main treatments for actinic keratoses in terms of complete clearance. 1